I had a work presentation at the Athens School of Fine Arts recently.
Two of the works, T-Gyroid and Shell, are both produced by Shapeways.
More information here.
Check a video on YouTube and some images on Flickr.

The wall thickness of the shell is about 1mm. Same as the T-Gyroid model.

I know exactly what you say, as I face the same problem each time I upload a model.
I am trying to use 1mm wall thickness, also I try to make my models' surfaces look like a "grid" or any similar grid surface, just to keep the price down.

However, whatever I tried on a 30cm model... gets immediately expensive...